1. Field of the Invention
The present invention is a CIP of application Ser. No. 12/413,582, filed Mar. 29, 2009 now abandoned, the entire contents of which are hereby incorporated by reference.
2. Description of the Prior Art
The JP Publication No. P2004-237420 discloses that a polygonal ball knob of a support member included in a tool joint is received in a receiving chamber of an acting head, and a shape of the receiving chamber is in response to that of the ball knob to form a polygon shape. Besides, a connection structure is used to engage the acting head with the support member together when the support member is pressed therein. When the support member is pulled out, the support member swings pivotally relative to the acting head.
However, because an inner wall of the receiving chamber is formed in a polygon shape, the ball knob contacts with the inner wall of the receiving chamber surface by surface. When a driving device is turned on, the acting head is driven to rotate at high speed by the support member so as to drive a threaded member to rotate. In working condition, driving force of the driving device may be increased to drive threaded member to rotate, so that the ball knob is always stuck and failed in the receiving chamber of the action head.
To avoid failure and inoperation of the knob and the acting head, a joint is provided in U.S. Pat. No. 5,069,569. The joint has a female part which is formed with a polygonal opening whose side surfaces includes several convex surfaces. Thus, edges of knob may not be crushed, scuffed, or wedged.
However, the female part of the joint described in U.S. Pat. No. 5,069,569 would be probably crushed easily because of its appearance. The circumferentially arranged surfaces of the opening of the female part are convex inwardly. Thus, corners between any two adjacent convex surfaces would be sharpened. Serious stress concentration would take the places where the corners are. As a result, the female part would be cracked or formed with rifts by a regular punching of rotation easily.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.